Sintered alloy article, its production method and a motorized fuel pump comprising a bearing comprised of sintered alloy article

ABSTRACT

A sintered alloy article having superior corrosion resistance while also ensuring product dimensional accuracy is provided. A sintered alloy body is formed by molding and sintering (S 2 ) a raw material powder containing copper, and tin plating (S 4 ) treatment on this sintered alloy body is performed, followed by sizing (S 5 ). When the tin plating layer is compressed during sizing, the tin plating layer is formed to a nearly uniform thickness, pores opened in the outer surface of the sintered alloy body are blocked by the above tin plating, as a result of said tin plating being compressed by the above sizing. Moreover, by combining a copper-based sintered alloy and tin plating, a sintered body is obtained provided with both corrosion resistance to sulfur and its compounds as well as corrosion resistance to formic acid, acetic acid and other organic acids.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a sintered alloy article, its production method and a motorized fuel pump comprising a bearing composed of sintered alloy article.

[0003] 2. Background Art

[0004] Motorized fuel pumps for gasoline engines of the prior art are known to have a structure as exemplified in the schematic cross-sectional drawing of FIG. 8. Namely, as shown in the drawing, the above fuel pump 1 has a structure such that, in a casing 2, a rotating shaft 2 arranged at both ends of a motor 3 is supported by bearings 5, an impeller 6 is inserted in one end of the above rotating shaft 4, and a narrow gasoline flow path 7 is formed along the outer peripheral surface of the above impeller 6 and a motor (armature) 3 and the space (not shown) between bearings 5 and rotating shaft 4. This motorized fuel pump operates such that impeller 6 rotates with the rotation of the above motor 3, gasoline is introduced into casing 2 with the rotation of this impeller 6, and the introduced gasoline is supplied into a separately arranged gasoline engine by passing through the gasoline flow path formed along the outer peripheral surface of impeller 6 and motor 3 and the space not shown between the bearings 5 and rotating shaft 4. Furthermore, in FIG. 8, a trace amount of fuel passes over the outer periphery of both bearings 5, and gasoline that has been increased in pressure by impeller 6 reaches the outer peripheral surface of motor 3 by passing through gasoline flow path 7 of casing 1.

[0005] A copper-based sintered alloy article is used for bearings 5 serving as structural members of the above fuel pump, and in the production of this sintered alloy article, a raw material powder containing copper is compressed to form a green compact, this green compact is then sintered to form a sintered alloy body, and this sintered alloy body is then sized by additional compression to obtain the prescribed dimensions.

[0006] Since the above bearings 5 are used in an environment in which they are exposed to fuel, a copper-based sintered alloy article, that comprises a raw material powder containing copper as previously described, is used in consideration of resistance to corrosion by fuel. However, even in the case of such a copper-based sintered alloy article, there is the problem of decreased service life due to corrosion if a fuel is used that contains sulfur or its compounds, or a fuel is used that contains formic acid, acetic acid or other organic acids.

[0007] Therefore, a copper-lead alloy bearing is described in Japanese Unexamined Patent Application, First Publication No. 5-202938A in which the providing of tin plating, lead plating or plating of an alloy thereof on the inner and outer surfaces of a copper alloy bearing is effective for improving the resistance of the bearing to corrosion (paragraph 0005 of the patent publication).

[0008] However, in products requiring a dimensional accuracy of, for example, 10 μm or less, even if dimensions are within the allowed dimensional tolerance by performing sizing prior to plating treatment, there is the problem of being unable to secure the required dimensional accuracy due to variations in the thickness of the plating performed thereafter.

BRIEF SUMMARY OF THE INVENTION

[0009] In order to solve the above problems, the object of the present invention is to provide a sintered alloy article having superior corrosion resistance and which is able to ensure product dimensional accuracy, its production method, and a motorized fuel pump that uses bearings composed of the sintered alloy article.

[0010] In order to achieve the above object, the present invention provide a sintered alloy article by providing a tin plating layer on a sintered alloy body comprised by molding and sintering a raw material powder containing copper, and sizing said sintered alloy body having this tin plating layer.

[0011] A sintered alloy article can be obtained that has high corrosion resistance by covering a copper-based sintered alloy body with a tin plating layer having corrosion resistance. In particular, corrosion resistance to both sulfur and its compounds as well as formic acid, acetic acid and other organic acids can be provided by combining a copper-based sintered alloy and tin plating. In addition, since the sintered alloy body having a tin plating layer is sized, product dimensions which include the tin plating layer can be finished to within a prescribed dimensional tolerance. Moreover, the tin plating layer is compressed by sizing, and the tin plating layer is formed to a nearly uniform thickness, while at the same time, the compressed tin plating layer blocks air holes in the outer surface of the sintered alloy body.

[0012] The above sintered alloy article may be a sliding member.

[0013] As a result, a sliding member is obtained that is provided with corrosion resistance to both sulfur and its compounds as well as formic acid, acetic acid and other organic acids.

[0014] The present invention also provide a method that comprises forming a sintered alloy body by molding and sintering a raw material powder containing copper, and tin plating this sintered alloy body followed by sizing.

[0015] As a result of using this method, since the tin plating layer is compressed during sizing, the tin plating layer is formed to a nearly uniform thickness, and at the same time, air holes opened in the outer surface of the sintered alloy body are covered by said tin plating due to said tin plating being compressed by the above sizing, the compressed tin plating layer blocks air holes in the outer surface of the sintered alloy article, and improves coverage by said tin plating layer. In addition, since a sintered alloy body having a tin plating layer is sized, product dimensions that include the tin plating layer can be finished to within a prescribed dimensional tolerance. Moreover, by combining a copper-based sintered alloy article and tin plating, a sintered alloy article is obtained that is provided with corrosion resistance to both sulfur and its compounds as well as formic acid, acetic acid and other organic acids.

[0016] The present invention further provides a motorized fuel pump that which comprises a bearing composed of the above sintered alloy article.

[0017] As a result, the bearings of this motorized fuel pump have an superior service life with respect to fuel containing sulfur and its compounds or fuel containing formic acid, acetic acid or other organic acids.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a flow chart that explains a production method indicating a first embodiment of the present invention.

[0019]FIG. 2 is a perspective view of a sintered alloy body of a first embodiment of the present invention.

[0020]FIG. 3 is a partially enlarged cross-sectional view of a sintered alloy article of a first embodiment of the present invention.

[0021]FIG. 4 is a cross-sectional view that explains sizing of a first embodiment of the present invention.

[0022]FIG. 5 is an enlarged cross-sectional view of a tin plating layer prior to sizing of a first embodiment of the present invention.

[0023]FIG. 6 is an enlarged cross-sectional view of a tin plating layer after sizing of a first embodiment of the present invention.

[0024]FIG. 7 is a flow chart that explains a production method indicating a second embodiment of the present invention.

[0025]FIG. 8 is a schematic cross-sectional view of a motorized fuel pump for a gasoline engine.

DETAILED DESCRIPTION OF THE INVENTION

[0026] The following provides an explanation of embodiments of the present invention with reference to the attached drawings. FIGS. 1 through 6 show one embodiment of the present invention, and Cu—Ni—Zn—C-based or Cu—Sn—C-based raw materials can be used for the raw material of the sintered alloy body. Furthermore, the following explanation is provided using the example of the above bearings 5 for the sintered alloy article. As shown in FIGS. 2 and 3, bearing 5 is composed of a roughly cylindrical sintered alloy body 51, and cylindrical sliding surface 52 over which the above rotating shaft 4 rotationally slides is formed in its center. Moreover, tin plating layer 53 is provided that covers the entire exposed outer surface of sintered alloy body 51. Furthermore, the tin plating in the present invention refers to that which contains plating of tin or tin alloy.

[0027] A composition containing, for example, 10 to 25% by weight of Zn, 10 to 25% by weight of Ni, 0.1 to 0.9% by weight of P and 1 to 8% by weight of C, with the remainder consisting of Cu and unavoidable impurities, and a graphite-dispersed Cu-based sintered alloy having porosity of 5 to 25% can be used for sintered alloy body 51 of the above bearing 5, while graphite-dispersed Cu-based sintered alloy having a composition other than that described above can also be used.

[0028] In providing an explanation of the production method of the bearing 5 with reference to FIG. 1, bearings 5 composed of a graphite-dispersed Cu-based sintered alloy were produced by preparing as the raw material powder used for sintered alloy body 51 five types of Cu—Ni—Zn alloy powders, all of which are formed by water atomization and which had an average particle diameter of 45 μm, namely Cu-15.8% Ni-18.3% Zn alloy powder, Cu-16.9% Ni-18.0% Zn alloy powder, Cu-18.8% Ni-18.4% Zn alloy powder, Cu-17.4% Ni-16.4% Zn alloy powder and Cu-17.3% Ni-19.9% Zn alloy powder, (thus five types of alloy powders), water-atomized Cu-P alloy (containing 33% P) powder having an average particle diameter of 45 μm, and graphite powder having an average particle diameter of 45 μm, blending these raw material powders to a prescribed blended composition, mixing for 40 minutes with a V mixer (S1: Step 1), molding into a green compact of a prescribed shape by compressing at a prescribed pressure within the range of 150 to 300 MPa (S2), and sintering this green compact in an ammonia decomposed gas atmosphere under conditions of holding for 40 minutes at a prescribed temperature within the range of 750 to 900° C. (S3). When the resulting bearings 5 were observed using a light microscope (magnification: 200×), the Cu—P alloy and graphite were finely dispersed in a base material composed of a solid solution phase of Cu—Ni—Zn alloy in all cases, and all exhibited a structure that contained pores. These bearings 5 made of graphite-dispersed Cu-based sintered alloys obtained in this manner demonstrated both the superior strength and corrosion resistance possessed by the Cu—Ni—Zn alloys that form their base materials, and also demonstrated superior wear resistance in an atmosphere exposed to highly pressurized, fast-flowing gasoline. In addition, a motorized fuel pump that uses these graphite-dispersed Cu-based sintered alloy bearings has a superior service life with respect to fuel containing sulfur or its compounds in its impurities.

[0029] In order to further improve corrosion resistance in the present invention, plating treatment (S4) is performed on sintered alloy body 51 following sintering treatment (S3). In this plating treatment (S4), a plating layer 53 containing tin (Sn) and having a thickness of about 2 to 25μ is formed on the outer surface of sintered alloy body 51 by electroplating and so forth.

[0030] Following plating treatment, bearing 5 is sized by recompressing (S5) to finish to prescribed dimensions. As an example, FIG. 4 shows a mold correcting apparatus 11 used for sizing. This mold correcting apparatus 11 uses the vertical direction as the axial direction (direction of the vertical axis of compression), and is equipped with die 12, core rod 13, lower punch 14 and upper punch 15. Die 12 has a nearly cylindrical shape, and nearly cylindrical core rod 13 is coaxially positioned within this die 12. Lower punch 14 has a nearly cylindrical shape, and is engaged between die 12 and core rod 13 so as to move up and down freely from below. Upper punch 15 has a nearly cylindrical shape, and is removably engaged between die 12 and core rod 13 so as to move up and down freely from above. As shown in FIG. 4, the above bearing 5 is loaded into die 12, and with core 13 inserted and arranged on sliding surface 52 that forms a through hole of this bearing 5, bearing 5 is pressurized by upper and lower punches 13 and 14 from above and below to correct to prescribed dimensions.

[0031] Here, in order to confirm the status of plating layer 53 before sizing and plating layer 53 after sizing, a plurality of sintered alloy bodies 51 were fabricated, and enlarged photographs of their structure were taken. In actuality, after forming 20 sintered alloy bodies 51 through plating treatment under identical conditions, sizing was performed on half, or 10, of the sintered alloy bodies 51.

[0032] These ten sintered alloy bodies 51 were then cut as shown in FIG. 3, and enlarged photographs of the structure of sliding surface 52 were taken. As a result, in the ten sintered alloy bodies 51 on which sizing was not performed, the average thickness of tin plating layer 53 on sliding surface 52 was about 10 μm, and in the ten sintered alloy bodies 51 on which sizing was performed, the average thickness of tin plating layer 53 was about 6 μm. In this manner, sizing causes the thickness of tin plating layer 53 to become thinner as a result of the tin plating layer being drawn out, and the openings 54A of pores 54 are blocked by this drawn out portion of tin plating layer 53.

[0033] In the sintered alloy bodies 51 on which sizing was not performed, as shown in FIG. 5, pores 54 having openings 54A are present in sliding surface 52, and these represent locations at which pore blockage by plating is inadequate. In addition, surface irregularities are observed in the outer surface of tin plating layer 53, and these surface irregularities are formed due to variations in the thickness of tin plating layer 53.

[0034] In contrast, in sintered alloy bodies 51 on which sizing was performed, as shown in FIG. 6, openings 54A of pores 54 present in sliding surface 52 are blocked by tin plating layer 53, while at the same time, there are few surface irregularities in the outer surface of tin plating layer 53.

[0035] In this manner, by performing sizing (S5) after plating, pores 54 opened in the outer surface of sintered alloy body 51 are blocked by tin plating 53 as a result of compressing and spreading out said tin plating layer 53, thereby improving coverage by tin plating layer 53. In addition, together with the outer surface of tin plating layer 53 being formed flat by sizing (S5), it can also be finished to a nearly uniform thickness.

[0036] In this manner, in the present embodiment, since a tin plating layer 53 is provided on a sintered alloy body 51 comprised by molding and sintering a raw material powder containing copper, and a bearing 5 is sized that has this tin plating layer 53, a bearing 5 can be obtained that is composed of a sintered alloy article that has obtained a high corrosion resistance.

[0037] In particular, by combining a copper-based sintered alloy with tin plating, bearing 5 can be provided with both corrosion resistance to sulfur and its compounds, as well as corrosion resistance to formic acid, acetic acid and other organic acids. In addition, since a sintered alloy body 51 having tin plating layer 53 is sized, product dimensions which include tin plating layer 53 can be finished to within a prescribed dimensional tolerance. Moreover, since tin plating layer 53 is compressed by sizing, simultaneous to tin plating 53 being formed to nearly a uniform thickness, the compressed tin plating layer 53 seals pores present in the outer surface of sintered alloy body 51, thereby resulting superior coverage by tin plating layer 53.

[0038] In addition, the above sintered alloy article may be a sliding member, e.g. a bearing 5, and the bearing 5 is obtained that is provided with both corrosion resistance to sulfur and its compounds and corrosion resistance to formic acid, acetic acid and other organic acids.

[0039] In this manner, in an embodiment of the present invention, since a sintered alloy body 51 is formed by molding and sintering a raw material powder containing copper, and this sintered alloy body 51 is tin plated followed by sizing, tin plating layer 53 is compressed during sizing, and tin plating layer 53 is formed to a nearly uniform thickness, while at the same time, pores 54 opened in the outer surface of sintered alloy body 51 are blocked by tin plating layer 53 as a result of said tin plating layer 53 being compressed by the above sizing, thereby allowing compressed tin plating layer 53 to seal pores in the outer surface of sintered alloy body 51 resulting in improved coverage by tin plating layer 53. In addition, since sintered body alloy 51 having tin plating layer 53 is sized, product dimensions matching tin plating layer 53 can be finished to within a prescribed dimensional tolerance. Moreover, by combining a copper-based sintered alloy article and tin plating, a sintered alloy article is obtained provided with both corrosion resistance to sulfur and its compounds as well as corrosion resistance to formic acid, acetic acid and other organic acids.

[0040] In this manner, in an embodiment of the present invention, since a bearing 5 composed of the sintered alloy article of the present invention is used, the bearing 5 of a motorized fuel pump has a superior service life with respect to fuel containing sulfur and its compounds or formic acid, acetic acid or other organic acids.

[0041]FIG. 7 shows a second embodiment of the present invention. In providing a detailed description while using the same reference numerals for the corresponding parts of the above first embodiment and omitting a detailed explanation thereof, in this example, as a result of performing sizing (S6) prior to plating sintered alloy body 51 obtained by sintering (S3) treatment, the above plating(S4) treatment is performed after finishing sintered alloy body 51 to prescribed dimensions, and sizing (S5) is then performed after plating (S4) treatment. By pre-compressing sintered alloy body 51 prior to plating treatment by sizing, a sintered alloy article can be produced having even higher dimensional accuracy.

[0042] Furthermore, the present invention is not limited to the above embodiments, and various variations of the present invention can be carried out. For example, the present invention can be applied to various raw material powders so long as they contain copper or copper alloy, and is not limited to the above. In addition, the bearing is not limited to that described in the embodiments, but rather the present invention can be applied to bearings of various shapes. In addition, the sliding member is also not limited to a bearing, but rather the present invention can be applied to various types of sliding members provided the member has a sliding portion.

[0043] The sintered alloy article of present invention is composed by providing a tin plating layer on a sintered alloy body comprised by molding and sintering a raw material powder containing copper, and then sizing this sintered alloy body having a tin plating layer, and is provided with both corrosion resistance to sulfur and its compounds as well as corrosion resistance to formic acid, acetic acid and other organic acids. In addition, since a sintered alloy body having a tin plating layer is sized, product dimensions which include the tin plating layer can be finished to within a prescribed dimensional tolerance.

[0044] When the above sintered alloy article is a sliding member, the sliding member is provided with both corrosion resistance to sulfur and its compounds as well as corrosion resistance to formic acid, acetic acid and other organic acids.

[0045] The production method of the sintered alloy article is a method in which a sintered alloy body is formed by molding and sintering a raw material powder containing copper, and then tin plating this sintered alloy body followed by sizing, wherein the tin plating layer is compressed during sizing, and simultaneous to the tin plating layer being formed to nearly a uniform thickness, the above tin plating is compressed by the above sizing, and pores opened in the outer surface of the sintered alloy body are blocked by said tin plating, thereby enabling the compressed tin plating layer to seal pores in the outer surface of the sintered alloy body, and improve coverage by the tin plating layer.

[0046] The motorized fuel pump of the present invention comprises a bearing comprised of the above sintered alloy article, and has a superior service life with respect to fuel containing sulfur and its compounds or formic acid, acetic acid and other organic acids. 

1. A sintered alloy article obtainable by providing a tin plating layer on a sintered alloy body comprised by molding and sintering a raw material powder containing copper, and sizing said sintered alloy body having this tin plating layer.
 2. The sintered alloy article according to claim 1 wherein, said sintered alloy article is a sliding member.
 3. A production method of a sintered alloy article comprising: forming a sintered alloy body by molding and sintering a raw material powder containing copper, and tin plating this sintered alloy body followed by sizing.
 4. A motorized fuel pump comprising a bearing composed of the sintered alloy article according to claim
 1. 